{"product_id":"penn-grade1-classic-gl-4-gear-oil-sae-80w-90-1-quart-4-pack-mineral-blend-for-yellow-metallurgy","title":"PENN GRADE1 Classic GL-4 Gear Oil SAE 80W-90 — 1 Quart 4-Pack, Mineral Blend for Yellow Metallurgy","description":"\u003cp\u003e\u003cstrong\u003ePENN GRADE1 Classic Multi-Purpose GL-4 Gear Oil SAE 80W-90 is a mineral-based transmission lubricant formulated for classic manual gearboxes and synchronizers that use yellow metallurgy.\u003c\/strong\u003e\u003c\/p\u003e\n\n\u003cp\u003eBuilt from carefully selected premium mineral base stocks and targeted additive technology, this GL-4 gear oil is intended for older manual transmissions, transaxles, and differentials where brass, bronze or copper components (synchronizers and bushings) require a formula without friction modifiers. Supplied as a convenient 1 quart bottle in a 4-pack, it covers routine service and top-ups for vintage vehicles, restorations, and classic car projects that specify GL-4 SAE 80W-90.\u003c\/p\u003e\n\n\u003ch3\u003eWhy choose a GL-4 SAE 80W-90 oil for older manuals?\u003c\/h3\u003e\n\u003cp\u003eGL-4 oils provide balanced extreme-pressure protection while avoiding friction modifiers found in GL-5 products that can interfere with synchronizer engagement. For transmissions that use softer metals, this formulation helps preserve shift feel and component life without introducing chemicals that change friction characteristics.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eFormulated explicitly for yellow metallurgy (brass\/bronze\/copper) in synchronizers\u003c\/li\u003e\n  \u003cli\u003eMineral-based blend for compatibility with vintage seals and components\u003c\/li\u003e\n  \u003cli\u003eMeets GL-4 performance needs without GL-5 friction modifiers\u003c\/li\u003e\n  \u003cli\u003eAvailable in 1 quart bottles packaged as a 4-pack for service convenience\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eHow does this oil affect shifting and synchronizer performance?\u003c\/h3\u003e\n\u003cp\u003eThis GL-4 SAE 80W-90 maintains stable friction characteristics that help synchronizers engage smoothly. Because it omits friction modifiers common in GL-5 oils, it reduces the risk of harsh or delayed shifts in gearboxes designed around older metallurgy.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003ePromotes consistent shift feel by preserving synchronizer friction characteristics\u003c\/li\u003e\n  \u003cli\u003eReduces risk of chatter or slipping caused by incompatible additives\u003c\/li\u003e\n  \u003cli\u003eHelps protect bushings and thrust washers made from soft metals\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eCan I use it in limited-slip differentials or modern gearboxes?\u003c\/h3\u003e\n\u003cp\u003eNo — this product is not formulated for limited-slip applications and does not contain the specialized friction modifiers required by many limited-slip designs. It also is not a substitute for GL-5 extreme-pressure oils where OEMs require that grade.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003eNot recommended for limited-slip differentials\u003c\/li\u003e\n  \u003cli\u003eNot suitable where API GL-5 or OEM-specified fluids are mandated\u003c\/li\u003e\n  \u003cli\u003eBest used in classic manuals, transaxles, and older differentials requiring GL-4\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003ch3\u003eWhat practical details should I know before buying?\u003c\/h3\u003e\n\u003cp\u003eThe product ships as four 1-quart bottles, giving you enough oil for several services or a full fluid change on many compact and classic vehicles. Store bottles upright in a cool, dry place and follow vehicle manufacturer service intervals and fill specifications.\u003c\/p\u003e\n\u003cul\u003e\n  \u003cli\u003ePack contains four 1-quart bottles for repeated service or multi-vehicle use\u003c\/li\u003e\n  \u003cli\u003eKeep upright and sealed until use to maintain formulation integrity\u003c\/li\u003e\n  \u003cli\u003eCheck your vehicle’s manual to confirm GL-4 SAE 80W-90 compatibility\u003c\/li\u003e\n\u003c\/ul\u003e\n\n\u003cp\u003eWho is this for: This PENN GRADE1 GL-4 SAE 80W-90 four-pack is aimed at classic car owners, restoration shops, hobbyists, and mechanics servicing older manual transmissions and transaxles that require oils compatible with brass, bronze, or copper synchronizers. If your vehicle requires modern GL-5 or specialized OEM fluids, choose a product specified by the manufacturer instead.\u003c\/p\u003e\n\u003csection class=\"product-faq-snippet\"\u003e\u003ch3\u003eFAQ\u003c\/h3\u003e\n\u003cdiv class=\"faq-item\"\u003e\n\u003cp class=\"faq-q\"\u003eQ: Is this oil safe for synchronizers made of brass or bronze?\u003c\/p\u003e\n\u003cp class=\"faq-a\"\u003eA: Yes — formulated for yellow metallurgy, it avoids friction modifiers that can harm synchronizer performance.\u003c\/p\u003e\n\u003c\/div\u003e\n\u003cdiv class=\"faq-item\"\u003e\n\u003cp class=\"faq-q\"\u003eQ: Can I use this in limited-slip differentials?\u003c\/p\u003e\n\u003cp class=\"faq-a\"\u003eA: No — this product lacks limited-slip friction modifiers and is not recommended for LSDs or where GL-5 is required.\u003c\/p\u003e\n\u003c\/div\u003e\u003c\/section\u003e","brand":"PENN GRADE1","offers":[{"title":"Default Title","offer_id":55168844530007,"sku":"B0CHG3X79B","price":79.43,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/1050\/1524\/7191\/files\/penn-grade1-front-label-1-quart-bottle.jpg?v=1790414750","url":"https:\/\/britishgarage.co.uk\/products\/penn-grade1-classic-gl-4-gear-oil-sae-80w-90-1-quart-4-pack-mineral-blend-for-yellow-metallurgy","provider":"British Garage","version":"1.0","type":"link"}